271 lines
12 KiB
C
271 lines
12 KiB
C
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//===- LiveRangeCalc.h - Calculate live ranges -----------------*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// The LiveRangeCalc class can be used to implement the computation of
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// live ranges from scratch.
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// It caches information about values in the CFG to speed up repeated
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// operations on the same live range. The cache can be shared by
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// non-overlapping live ranges. SplitKit uses that when computing the live
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// range of split products.
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//
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// A low-level interface is available to clients that know where a variable is
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// live, but don't know which value it has as every point. LiveRangeCalc will
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// propagate values down the dominator tree, and even insert PHI-defs where
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// needed. SplitKit uses this faster interface when possible.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_LIB_CODEGEN_LIVERANGECALC_H
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#define LLVM_LIB_CODEGEN_LIVERANGECALC_H
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#include "llvm/ADT/ArrayRef.h"
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#include "llvm/ADT/BitVector.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/IndexedMap.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/CodeGen/LiveInterval.h"
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#include "llvm/CodeGen/MachineBasicBlock.h"
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#include "llvm/CodeGen/SlotIndexes.h"
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#include "llvm/MC/LaneBitmask.h"
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#include <utility>
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namespace llvm {
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template <class NodeT> class DomTreeNodeBase;
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class MachineDominatorTree;
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class MachineFunction;
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class MachineRegisterInfo;
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using MachineDomTreeNode = DomTreeNodeBase<MachineBasicBlock>;
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class LiveRangeCalc {
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const MachineFunction *MF = nullptr;
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const MachineRegisterInfo *MRI = nullptr;
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SlotIndexes *Indexes = nullptr;
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MachineDominatorTree *DomTree = nullptr;
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VNInfo::Allocator *Alloc = nullptr;
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/// LiveOutPair - A value and the block that defined it. The domtree node is
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/// redundant, it can be computed as: MDT[Indexes.getMBBFromIndex(VNI->def)].
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using LiveOutPair = std::pair<VNInfo *, MachineDomTreeNode *>;
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/// LiveOutMap - Map basic blocks to the value leaving the block.
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using LiveOutMap = IndexedMap<LiveOutPair, MBB2NumberFunctor>;
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/// Bit vector of active entries in LiveOut, also used as a visited set by
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/// findReachingDefs. One entry per basic block, indexed by block number.
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/// This is kept as a separate bit vector because it can be cleared quickly
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/// when switching live ranges.
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BitVector Seen;
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/// Map LiveRange to sets of blocks (represented by bit vectors) that
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/// in the live range are defined on entry and undefined on entry.
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/// A block is defined on entry if there is a path from at least one of
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/// the defs in the live range to the entry of the block, and conversely,
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/// a block is undefined on entry, if there is no such path (i.e. no
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/// definition reaches the entry of the block). A single LiveRangeCalc
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/// object is used to track live-out information for multiple registers
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/// in live range splitting (which is ok, since the live ranges of these
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/// registers do not overlap), but the defined/undefined information must
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/// be kept separate for each individual range.
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/// By convention, EntryInfoMap[&LR] = { Defined, Undefined }.
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using EntryInfoMap = DenseMap<LiveRange *, std::pair<BitVector, BitVector>>;
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EntryInfoMap EntryInfos;
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/// Map each basic block where a live range is live out to the live-out value
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/// and its defining block.
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///
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/// For every basic block, MBB, one of these conditions shall be true:
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///
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/// 1. !Seen.count(MBB->getNumber())
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/// Blocks without a Seen bit are ignored.
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/// 2. LiveOut[MBB].second.getNode() == MBB
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/// The live-out value is defined in MBB.
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/// 3. forall P in preds(MBB): LiveOut[P] == LiveOut[MBB]
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/// The live-out value passses through MBB. All predecessors must carry
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/// the same value.
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///
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/// The domtree node may be null, it can be computed.
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///
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/// The map can be shared by multiple live ranges as long as no two are
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/// live-out of the same block.
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LiveOutMap Map;
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/// LiveInBlock - Information about a basic block where a live range is known
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/// to be live-in, but the value has not yet been determined.
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struct LiveInBlock {
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// The live range set that is live-in to this block. The algorithms can
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// handle multiple non-overlapping live ranges simultaneously.
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LiveRange &LR;
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// DomNode - Dominator tree node for the block.
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// Cleared when the final value has been determined and LI has been updated.
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MachineDomTreeNode *DomNode;
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// Position in block where the live-in range ends, or SlotIndex() if the
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// range passes through the block. When the final value has been
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// determined, the range from the block start to Kill will be added to LI.
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SlotIndex Kill;
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// Live-in value filled in by updateSSA once it is known.
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VNInfo *Value = nullptr;
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LiveInBlock(LiveRange &LR, MachineDomTreeNode *node, SlotIndex kill)
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: LR(LR), DomNode(node), Kill(kill) {}
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};
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/// LiveIn - Work list of blocks where the live-in value has yet to be
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/// determined. This list is typically computed by findReachingDefs() and
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/// used as a work list by updateSSA(). The low-level interface may also be
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/// used to add entries directly.
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SmallVector<LiveInBlock, 16> LiveIn;
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/// Check if the entry to block @p MBB can be reached by any of the defs
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/// in @p LR. Return true if none of the defs reach the entry to @p MBB.
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bool isDefOnEntry(LiveRange &LR, ArrayRef<SlotIndex> Undefs,
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MachineBasicBlock &MBB, BitVector &DefOnEntry,
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BitVector &UndefOnEntry);
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/// Find the set of defs that can reach @p Kill. @p Kill must belong to
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/// @p UseMBB.
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///
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/// If exactly one def can reach @p UseMBB, and the def dominates @p Kill,
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/// all paths from the def to @p UseMBB are added to @p LR, and the function
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/// returns true.
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///
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/// If multiple values can reach @p UseMBB, the blocks that need @p LR to be
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/// live in are added to the LiveIn array, and the function returns false.
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///
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/// The array @p Undef provides the locations where the range @p LR becomes
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/// undefined by <def,read-undef> operands on other subranges. If @p Undef
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/// is non-empty and @p Kill is jointly dominated only by the entries of
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/// @p Undef, the function returns false.
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///
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/// PhysReg, when set, is used to verify live-in lists on basic blocks.
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bool findReachingDefs(LiveRange &LR, MachineBasicBlock &UseMBB, SlotIndex Use,
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unsigned PhysReg, ArrayRef<SlotIndex> Undefs);
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/// updateSSA - Compute the values that will be live in to all requested
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/// blocks in LiveIn. Create PHI-def values as required to preserve SSA form.
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///
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/// Every live-in block must be jointly dominated by the added live-out
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/// blocks. No values are read from the live ranges.
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void updateSSA();
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/// Transfer information from the LiveIn vector to the live ranges and update
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/// the given @p LiveOuts.
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void updateFromLiveIns();
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protected:
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/// Some getters to expose in a read-only way some private fields to
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/// subclasses.
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const MachineFunction *getMachineFunction() { return MF; }
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const MachineRegisterInfo *getRegInfo() const { return MRI; }
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SlotIndexes *getIndexes() { return Indexes; }
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MachineDominatorTree *getDomTree() { return DomTree; }
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VNInfo::Allocator *getVNAlloc() { return Alloc; }
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/// Reset Map and Seen fields.
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void resetLiveOutMap();
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public:
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LiveRangeCalc() = default;
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//===--------------------------------------------------------------------===//
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// High-level interface.
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//===--------------------------------------------------------------------===//
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//
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// Calculate live ranges from scratch.
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//
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/// reset - Prepare caches for a new set of non-overlapping live ranges. The
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/// caches must be reset before attempting calculations with a live range
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/// that may overlap a previously computed live range, and before the first
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/// live range in a function. If live ranges are not known to be
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/// non-overlapping, call reset before each.
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void reset(const MachineFunction *mf, SlotIndexes *SI,
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MachineDominatorTree *MDT, VNInfo::Allocator *VNIA);
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//===--------------------------------------------------------------------===//
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// Mid-level interface.
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//===--------------------------------------------------------------------===//
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//
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// Modify existing live ranges.
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//
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/// Extend the live range of @p LR to reach @p Use.
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///
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/// The existing values in @p LR must be live so they jointly dominate @p Use.
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/// If @p Use is not dominated by a single existing value, PHI-defs are
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/// inserted as required to preserve SSA form.
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///
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/// PhysReg, when set, is used to verify live-in lists on basic blocks.
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void extend(LiveRange &LR, SlotIndex Use, unsigned PhysReg,
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ArrayRef<SlotIndex> Undefs);
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//===--------------------------------------------------------------------===//
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// Low-level interface.
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//===--------------------------------------------------------------------===//
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//
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// These functions can be used to compute live ranges where the live-in and
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// live-out blocks are already known, but the SSA value in each block is
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// unknown.
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//
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// After calling reset(), add known live-out values and known live-in blocks.
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// Then call calculateValues() to compute the actual value that is
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// live-in to each block, and add liveness to the live ranges.
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//
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/// setLiveOutValue - Indicate that VNI is live out from MBB. The
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/// calculateValues() function will not add liveness for MBB, the caller
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/// should take care of that.
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///
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/// VNI may be null only if MBB is a live-through block also passed to
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/// addLiveInBlock().
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void setLiveOutValue(MachineBasicBlock *MBB, VNInfo *VNI) {
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Seen.set(MBB->getNumber());
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Map[MBB] = LiveOutPair(VNI, nullptr);
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}
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/// addLiveInBlock - Add a block with an unknown live-in value. This
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/// function can only be called once per basic block. Once the live-in value
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/// has been determined, calculateValues() will add liveness to LI.
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///
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/// @param LR The live range that is live-in to the block.
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/// @param DomNode The domtree node for the block.
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/// @param Kill Index in block where LI is killed. If the value is
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/// live-through, set Kill = SLotIndex() and also call
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/// setLiveOutValue(MBB, 0).
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void addLiveInBlock(LiveRange &LR, MachineDomTreeNode *DomNode,
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SlotIndex Kill = SlotIndex()) {
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LiveIn.push_back(LiveInBlock(LR, DomNode, Kill));
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}
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/// calculateValues - Calculate the value that will be live-in to each block
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/// added with addLiveInBlock. Add PHI-def values as needed to preserve SSA
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/// form. Add liveness to all live-in blocks up to the Kill point, or the
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/// whole block for live-through blocks.
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///
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/// Every predecessor of a live-in block must have been given a value with
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/// setLiveOutValue, the value may be null for live-trough blocks.
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void calculateValues();
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/// A diagnostic function to check if the end of the block @p MBB is
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/// jointly dominated by the blocks corresponding to the slot indices
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/// in @p Defs. This function is mainly for use in self-verification
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/// checks.
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LLVM_ATTRIBUTE_UNUSED
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static bool isJointlyDominated(const MachineBasicBlock *MBB,
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ArrayRef<SlotIndex> Defs,
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const SlotIndexes &Indexes);
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};
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} // end namespace llvm
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#endif // LLVM_LIB_CODEGEN_LIVERANGECALC_H
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